1. Field of the Invention
This invention relates to the field of radar target simulators and more particularly, to such simulators which simulate ‘complex’ radar targets.
2. Discussion of Prior Art
Hardware in the loop (HWIL or HIL) testing of missiles with active radio frequency (RF) seekers requires the accurate simulation of targets which the seeker or seekers is likely to encounter in service. Such testing is of course significantly cheaper that the live fire testing of such missile systems and as such a significant body of research is now directed towards the development of accurate simulation HWIL test facilities.
A Complex target can be described as a more lifelike target such as an aircraft with its associated extended structure as opposed to a more simple target such as a flat plate reflector or a trihedral corner.
Complex target emitters are used to generate RF signals in space to simulate radar returns from complex radar targets such returns including characteristics such as target scintillation and angle glint fluctuation along with the simulation of radar clutter.
The radar return from a complex radar target fluctuates as the relative positions and orientations of target and seeker change. This is due to effects in the backscatter associated with complex reflecting surfaces. An RF radar seeker must detect its target and provide continuous estimates of the target direction in order to steer a missile to a hit. Target signal fluctuations can influence both the ability to detect the target and the accuracy of any direction measurements.
State of the art radar complex target emitters stimulate their targets by the effective random movement of a bright spot which the seeker tracks. Such emitters provide the effective movement of a bright spot by the use of the controlled variation of the amplitude of RF emissions from typically three or four emitter horns. In order to simulate the required control of the wave front produced by such a system the amplitudes of the emitter horns are varied so as to effectively tilt the wave front.
The phase relationship between the emitter horns in such a system is fixed and therefore the mechanism by which the effective movements of the bright spot are controlled relies solely on the variation of the respective amplitudes generated at the emitter horns and not by virtue of any phase relationship.
State of the art RF seekers may have several receiver channels and therefore in order to provide an accurate simulation of a clutter signal a clutter generator must be able to excite all receiver channels. The current state of the art mechanism by which clutter is introduced into a simulated radar target is by utilising a single RF emitter horn. Such an input can only provide a single angle from which a seeker can receive a signal thereby not producing any angular field change representative of a true return from distributed clutter.